Conventionally, when an internal combustion engine is started and exhaust gas emitted from the engine is low in temperature, an air pump is operated to generate secondary air. The secondary air is introduced into a three-way catalyst converter. Exhaust gas, which is emitted from the engine, is purified in the three-way catalyst converter, so that a three-way catalyst is activated. Secondary air is press-fed from the air pump, and is introduced into the three-way catalyst converter through a secondary air passage. A solenoid secondary-air control valve is provided in the secondary air passage.
The solenoid secondary-air control valve includes a solenoid valve and a check valve. The solenoid valve opens and closes the secondary air passage. The check valve restricts exhaust air emitted by the engine from flowing backward into the solenoid valve. As disclosed in JP-A-2002-260919 and JP-A-2002-272080, the solenoid valve is constructed of a valve body, a solenoid actuator, a coil spring, and the like. The valve body opens and closes an opening, i.e., a valve port that is formed in an intermediate portion of the secondary air passage. The solenoid actuator drives the valve body in the direction, in which the valve port is opened. The coil spring urges the valve in the direction, in which the valve port is closed.
A secondary air supply apparatus having the above structure includes a diagnostic function that determines a failure of the air pump and a failure of the solenoid valve. The diagnostic function determines a failure to be caused, when pressure of secondary air passing through the secondary air passage is out of a predetermined pressure range.
As shown in FIG. 4, a pressure sensor 101, which detects secondary air pressure, and a solenoid type air control valve, in which a solenoid valve 102 is integrated with a check valve 103, are components separated from each other. Accordingly, a mounting space, in which the secondary air supply apparatus is mounted, becomes large. Here, a pressure sensor 101 may be additionally provided to the solenoid secondary-air control valve disclosed in JP-A-2002-260919 and JP-A-2002-272080, so that the solenoid secondary-air control valve and the pressure sensor 101 may be produced as one assembly. The solenoid valve 102 includes a poppet valve 104, a solenoid coil 110, a stator core 111, a yoke 112, a moving core 113, and the like. The stator core 111 constructs a magnetic circuit with the solenoid coil 110. The solenoid coil 110 drives the poppet valve 104 in the direction, in which the poppet valve 104 opens a valve port. The check valve 103 includes a lead valve 114, a valve body 115, and a stopper 116.
However, when the pressure sensor 101 is additionally provided to the solenoid secondary-air control valve in the structure shown in FIG. 4, a sensor-mounting portion 106, in which the pressure sensor 101 is mounted, needs to be formed in the solenoid valve 102. Specifically, the sensor-mounting portion 106 needs to be formed in the inner space of the solenoid valve 102 and on the surface of the outer wall of a housing 105 of the solenoid valve 102. Accordingly, a housing, which is conventionally used, cannot be applied to this structure. Thus, the housing 105, which has the shape capable of mounting the sensor, needs to be manufactured. Furthermore, a pressure detecting male connector 121 and a solenoid-valve male connector 122 need to be provided to the solenoid valve 102. The pressure detecting male connector 121 includes a terminal that electrically connects the pressure sensor 101 with an engine control unit. The solenoid-valve male connector 122 electrically connects the solenoid valve 102 with the engine control unit.
Besides, a mounting space becomes large due to an additional mass of the pressure sensor 101. Accordingly, a pressure detecting female connector, which is provided on the side of the tip end of the vehicular wire harness, becomes hard to be mechanically connected with the pressure detecting male connector 121 in a narrow engine room. Besides, a solenoid-valve female connector, which is provided on the side of the tip end of the vehicular wire harness, becomes hard to be mechanically connected with the solenoid-valve male connector 122 in the narrow engine room. Additionally, a joint member such as a screw 107 needs to be provided for fixing the pressure sensor 101 to the sensor-mounting portion 106 of the housing 105 in the solenoid valve 102. Thus, when the pressure sensor 101 is additionally provided to the solenoid secondary-air control valve shown in FIG. 4, manufacturing cost may increase due to additional components and due to additional manufacturing processes.
In view of the foregoing problems, a pressure sensor, which includes a semiconductor pressure detecting element, may be integrated with a solenoid valve, which opens and closes a detection passage of fluid, to construct a pressure sensor integrated solenoid valve. As disclosed in JP-B2-3345306 (U.S. Pat. No. 5,925,826), the pressure sensor integrated solenoid valve may be applied to the secondary air supply apparatus. The pressure sensor is received in a sealed space that is constructed of a base and a cap in the pressure sensor integrated solenoid valve. The pressure sensor is arranged such that a semiconductor pressure detecting element partitions a standard pressure chamber and a fluid introducing chamber. A ceramic substrate covers the pressure sensor. An amplifier circuit, which amplifies a signal output from the pressure sensor, is provided to the inside of the ceramic substrate.
However, the detection passage of fluid extends through the inside the stator core, which constructs the magnetic circuit with the solenoid coil, in the structure of the pressure sensor integrated solenoid valve disclosed in U.S. Pat. No. 5,925,826. The semiconductor pressure detecting element is apt to cause a measurement error due to variation in temperature, accordingly, the semiconductor pressure detecting element is not suitable for detecting fluid in high temperature.
Additionally, foreign matters, which are contained in fluid passing through the detection fluid passage, may intrude into the fluid introducing chamber through a pressure introducing port and the detection passage of fluid. The foreign matters may adhere onto the amplifier circuit, which is exposed to the inside the fluid introducing chamber, and the amplifier circuit may output an abnormal signal. Furthermore, the pressure sensor is accommodated in the sealed space constructed of the base and the cap. Accordingly, a large number of sealing members such as O-rings and glue are needed for maintaining airtightness of the sealed space. As a result, manufacturing cost increases due to increase of the number of components and manufacturing processes.
Furthermore, in the structure of the pressure sensor integrated solenoid valve disclosed in U.S. Pat. No. 5,925,826, a terminal on the side of the pressure sensor is held by a terminal holder integrated with the cap, and another terminal on the side of the solenoid valve is held by a terminal holder integrated with the cap. Each terminal holder is fitted with a cylindrical male connector. The terminal holder, which holds the terminal on the side of the pressure sensor, is integrated with an end periphery of the cap. The end periphery of the cap is engaged with an engage groove, and is fixed with the base using glue. Accordingly, the position of the terminal on the side of the pressure sensor may be varied with respect to the position of the terminal on the side of the solenoid valve due to variation in dimension of the components. As a result, a female connector, which is provided to the tip end of a wire harness on the side of a control apparatus, may not be connected with the male connector.